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<title>Debugging with GDB: BSD libkvm Interface</title>

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<a name="BSD-libkvm-Interface-1"></a>
<h4 class="subsection">21.1.1 BSD libkvm Interface</h4>

<a name="index-libkvm"></a>
<a name="index-kernel-memory-image"></a>
<a name="index-kernel-crash-dump"></a>

<p>BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
interface that provides a uniform interface for accessing kernel virtual
memory images, including live systems and crash dumps.  <small>GDB</small>
uses this interface to allow you to debug live kernels and kernel crash
dumps on many native BSD configurations.  This is implemented as a
special <code>kvm</code> debugging target.  For debugging a live system, load
the currently running kernel into <small>GDB</small> and connect to the
<code>kvm</code> target:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) <b>target kvm</b>
</pre></div>

<p>For debugging crash dumps, provide the file name of the crash dump as an
argument:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) <b>target kvm /var/crash/bsd.0</b>
</pre></div>

<p>Once connected to the <code>kvm</code> target, the following commands are
available:
</p>
<dl compact="compact">
<dd><a name="index-kvm"></a>
</dd>
<dt><code>kvm pcb</code></dt>
<dd><p>Set current context from the <em>Process Control Block</em> (PCB) address.
</p>
</dd>
<dt><code>kvm proc</code></dt>
<dd><p>Set current context from proc address.  This command isn&rsquo;t available on
modern FreeBSD systems.
</p></dd>
</dl>




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